1. Field of the Invention
The present invention relates to a method for forming a liquid crystal display including a color filter with a light-shielding film.
2. Description of the Related Art
A light-shielding film is a black edge portion formed, in order to prevent light from leaking, around red, blue and green pixels of a color filter and around the color filter, and a dot-like or linear black pattern for shielding a thin film transistor (TFT) from light.
In a color filter used in a color liquid crystal display, pigmented pixel layers having red (R), green (G) or blue (B) color are formed on a transparent substrate. Moreover, in order to improve display contrast, a light-shielding film for a display is formed in gaps between the respective pigmented pixels of red, green and blue. In particular, in a liquid crystal display element of an active matrix drive system that includes a thin film transistor (TFT), in order to prevent image quality from deteriorating owing to an electric current leakage in the thin film transistor caused by light, the light-shielding film for a display is required to have high light-shielding property (optical density).
In order to manufacture a light-shielding film for a display with high light-shielding property, usage of metal has been considered. As a technique for manufacturing a light-shielding film for a display using fine metal particles, a technique for generating fine nickel particles in a layer by using a plating technique has already been disclosed (Japanese Patent Application Laid-Open (JP-A) No. 5-303090).
However, the method requires complicated operations of precipitating fine particles from a plating solution containing metal ions. Moreover, processing of a waste plating solution is also complicated and greatly affects the environment.
On the other hand, a method for manufacturing a light-shielding film for a display that does not use the plating technique is known. An example thereof is a technique of forming a light-shielding film for a display by using carbon black in place of fine metal particles (JP-A No. 62-9031).
However, carbon black has lower optical density per unit coating amount than fine metal particles. Accordingly, when high light-shielding property and optical density are ensured, a film inevitably becomes thicker. Therefore, when red, blue and green pixels are formed after formation of the light-shielding film for a display, uniform pixels are difficult to form.
Furthermore, as another technique in which a light-shielding film for a display is formed by using a plating technique, a method in which a metal thin film is formed by using a vacuum evaporation method or a sputtering method, whereby a photoresist is coated on the metal thin film, exposed to light through a photomask having the pattern of a light-shielding film for a display and developed, exposed areas of the metal thin film are etched, and the resist layer on the light-shielding film for a display is removed (See “Color TFT Liquid Crystal Display”, Kyoritsu Shuppan Co., Ltd, Jul. 20, 1996, pp. 218–220) can be used to form a film of a metal such as chromium as a light-shielding layer.
Since a metal film is used in the method, high light-shielding property can be obtained even if a film thickness is small. However, since the method requires usage of the vacuum evaporation method or the sputtering method which involves vacuum deposition processes and etching processes, costs increase and measures are necessary to prevent adverse influence on the environment. Furthermore, the metal film has high reflectance, and therefore display contrast decreases under strong ambient light. In order to prevent such a problem, a chromium film having a low reflectance (one made of two layers of chromium metal and chromium oxide) can be used; however, further cost increases are incurred.
A method for forming a light-shielding film including fine metal sulfide particles by using plating is known (See JP-A No. 7-218715). However, since the method also uses a plating technique, the method also has a problem of a waste solution affecting the environment and requires complicated processes, and is therefore unsatisfactory.
Accordingly, there is a need for an inexpensive method for manufacturing a thin light-shielding film for a display with high light-shielding performance.